RAFAH, GAZA STRIP -- Israeli forces pushed deeper into Gaza's southern city of Rafah on Sunday and battled Hamas in parts of the devastated north that the military said it had cleared months ago but where militants have regrouped.

Rafah is considered the last refuge in Gaza for more than a million civilians as well as Hamas' last stronghold. Some 300,000 people have fled the city following evacuation orders from Israel, which says it must invade to dismantle Hamas and return scores of hostages taken in the Oct. 7 attack against Israel that sparked the war.

Neighboring Egypt issued its strongest objection yet to the Rafah offensive, saying it intends to formally join South Africa's case at the International Court of Justice alleging Israel is committing genocide in Gaza, which Israel rejects. The foreign ministry statement cited “the worsening severity and scope of the Israeli attacks against Palestinian civilians.”

“A full-scale offensive on Rafah cannot take place,” United Nations human rights chief Volker Turk said in a statement, adding he cannot see how it can be reconciled with international humanitarian law.

U.S. Secretary of State Antony Blinken reiterated opposition to a major military assault on Rafah, and told CBS that Israel would “be left holding the bag on an enduring insurgency” without an exit from Gaza and postwar governance plan.

Gaza has been left without a functioning government, leading to a breakdown in public order and allowing Hamas' armed wing to reconstitute itself in even the hardest-hit areas. Israel has yet to offer a detailed plan for postwar governance in Gaza, saying only that it will maintain open-ended security control over the enclave of about 2.3 million Palestinians.

Internationally mediated talks over a cease-fire and hostage release appeared to be at a standstill.

Prime Minister Benjamin Netanyahu in a Memorial Day speech vowed to continue fighting until victory in memory of those killed in the war.

Netanyahu has rejected postwar plans proposed by the United States for the Palestinian Authority, which administers parts of the Israeli-occupied West Bank, to govern Gaza with support from Arab and Muslim countries. Those plans depend on progress toward the creation of a Palestinian state, which Netanyahu's government opposes.

The Oct. 7 attack killed around 1,200 people, mostly civilians, and took another 250 hostage. Militants still hold about 100 captives and the remains of more than 30.

Israel’s air, land and sea offensive has killed more than 35,000 Palestinians, mostly women and children, according to Gaza’s Health Ministry, which doesn’t distinguish between civilians and combatants in its figures. Israel says it has killed over 13,000 militants, without providing evidence.

Heavy bombardment in the north

Palestinians reported heavy Israeli bombardment overnight in the urban Jabaliya refugee camp and other areas in northern Gaza, which has been largely isolated by Israeli forces for months. UN officials say there is a “full-blown famine” there.

Residents said Israeli warplanes and artillery struck across the camp and the Zeitoun area east of Gaza City, where troops have battled militants for over a week. They have called on tens of thousands of people to relocate to nearby areas.

“It was a very difficult night,” said Abdel-Kareem Radwan, a 48-year-old from Jabaliya. He said they could hear intense and constant bombing since midday Saturday. “This is madness.”

First responders with the Palestinian Civil Defense said they were unable to respond to multiple calls for help from both areas, as well as from Rafah.

Rear Adm. Daniel Hagari, the top Israeli military spokesman, said forces were also operating in the northern towns of Beit Lahiya and Beit Hanoun, which were heavily bombed in the war's opening days.

“Hamas’ regime cannot be toppled without preparing an alternative to that regime,” columnist Ben Caspit wrote in Israel’s Maariv daily, channeling the growing frustration felt by many Israelis more than seven months into the war. “The only people who can govern Gaza after the war are Gazans, with a lot of support and help from the outside.”

Civilians flee in the south

The UN agency for Palestinian refugees, the main provider of aid in Gaza, said 300,000 people have fled Rafah since the operation began there. Most are heading to the heavily damaged nearby city of Khan Younis or Mawasi, a coastal tent camp where some 450,000 people are already living in squalid conditions.

Israel has now evacuated the eastern third of Rafah, which had been sheltering some 1.3 million Palestinians, most of whom had fled fighting elsewhere. The UN has warned that a planned full-scale invasion would further cripple humanitarian operations and cause a surge in civilian deaths.

The main aid entry points near Rafah are already affected. Israeli troops have captured the Gaza side of the Rafah crossing, forcing it to shut down. Egypt has refused to coordinate with Israel on the delivery of aid though the crossing because of “the unacceptable Israeli escalation,” the state-owned Al Qahera News channel reported.

A senior Egyptian official told The Associated Press that Cairo has lodged protests with Israel, the United States and European governments, saying the offensive has put its decades-old peace treaty with Israel — a cornerstone of regional stability — at high risk. The official was not authorized to brief media and spoke on condition of anonymity.

U.S. President Joe Biden has said he won't provide offensive weapons to Israel for Rafah, and his administration says there is “reasonable” evidence that Israel had breached international law protecting civilians.

Israel rejects those allegations, saying it tries to avoid harming civilians. It blames Hamas for the high toll because the militants fight in dense, residential areas.

In the Israeli-occupied West Bank, where deadly violence has increased since the war began, the Palestinian Health Ministry said a man was shot dead by Israeli forces in Balata refugee camp in Nablus. The army said its forces responded with live fire after being shot at by militants in the camp.

Krauss reported from Jerusalem and Magdy from Cairo. Associated Press writer Jack Jeffery in Jerusalem contributed.